1. Field of the Invention
The present invention relates to control signal generating circuits, and particularly to a power supply control signal generating circuit in a computer.
2. Description of Related Art
AT-style computer cases have a power button that is directly connected to the system computer power supply (PSU). The general configuration is a double-pole latching mains voltage switch with the four pins connected to wires from a four-core cable. The wires are either soldered to the power button (making it difficult to replace the power supply if it fails) or blade receptacles are used. An ATX power supply does not directly connect to the system power button, allowing the computer to be turned off via software. However, many ATX power supplies have a manual switch on the back to ensure the computer is truly off and no power is sent to the components. With this switch on, energy still flows to the components even when the computer appears to be “off.” This is known as soft-off or standby and can be used for remote wake up through Wake-on-Ring or Wake-on-LAN, but is generally used to power on the computer through a front switch. When the front switch is pressed, a MOSFET on a motherboard of the computer turns off, and then an input-output (I/O) controller on the motherboard converts the signal output from the MOSFET to a power supply control signal Power Supply On (PS_ON). The power supply control signal is then transmitted to the ATX power supply to control output of direct current (DC) voltage. However, when the user presses the front switch, static electricity that may have accumulated in the user's body is transmitted to the gate of the MOSFET through the front switch. The MOSFET has high input impedance, so a lot of static electricity can accumulate at the gate of the MOSFET and ruin the MOSFET.
What is needed, therefore, is to provide a power supply control signal generating circuit which can eliminate static electricity at the gate of the MOSFET.